that case they would be liable to snap, just as does the blade of a foil when undue pressure is brought to bear upon it. Moreover, the operation of sharpening would be extremely difficult.

So the blade of the chisel is merely faced with a thin plate of hardened steel, the remainder being of softer material.

Now, it is not at all likely that the unknown inventor of the modern chisel was aware of the analogy between art and nature, and would probably have been very much surprised if anyone had stated that he had borrowed his idea from the incisor teeth of the water-rat.

Yet he might have done so, for these teeth are almost wholly formed of ordinary tooth matter, and are faced with a thin plate of hard enamel, which exactly corresponds with the hardened steel facing of a chisel.

Any of my readers who possess skates will find, on examination, that the greater part of the blade is, in reality, soft iron, the steel, which comes upon the ice, being scarcely a fifth of an inch in length.